How to know a model has been clicked on?

First time game developer but 10 yr plus veteran with application and C# development.

How can you detect when you click on the screen you picked a model?
Is there a sample somewhere?

Sorry for the noob question.

Easiest way to do that is to use the physic engine. Have a look at the Raycasting physic sample.

Follow the raycasting sample project. Basically what you do is cast a ray from the mouse point outwards and get the hitresult. From the hitresult, you will know what gameobject the ray collided with.